US 6913320 B2
A free-blast method for extracting ore from an ore vein deposit wherein the vein is extracted by causing the ore comprised between the rock walls bordering the vein to spall into fragments. The ore fragments are recuperated as by aspiration and subsequently processed to retrieve the precious mineral.
1. A process for extracting ore from a vein having opposed sidewalls, comprising the steps of a) drilling pilot holes directly in the vein at specific intervals therealong, b) using thermal fragmentation, enlarging the pilot holes until the vein is fragmented, and c) recuperating by aspiration the fragmented ore along the vein.
2. A process as defined in
3. A process as defined in
4. A process as defined in
5. A process as defined in
6. A process as defined in
7. A method for extracting ore from an ore vein deposit, comprising the steps of a) establishing the location of the rock walls bordering the ore vein deposit, b) drilling pilot holes directly in the vein at specific intervals therealong, the intervals being determined as a function of the width of the vein, and using thermal fragmentation, enlarging the pilot holes until the vein is fragmented, and c) retrieving the fragments.
8. A method as defined in
9. A method as defined in
10. A method as defined in
11. A process for extracting ore from a vein having opposed sidewalls, comprising the steps of a) drilling pilot holes directly in the vein at specific intervals therealong, b) using thermal fragmentation, enlarging the pilot holes until the vein is fragmented, and c) recuperating the fragmented ore along the vein, wherein along at least a portion of the length of the vein, the pilot holes are successively enlarged according to a predetermined pattern wherein every other pilot hole is enlarged to a greater extent so as to merge with opposed adjacent pilot holes which have been previously enlarged.
1. Field of the Invention
The present invention relates to ore extraction and, more particularly, to thermal fragmentation mining for extracting ore from narrow-veins.
2. Description of the Prior Art
For many years, mine operators have worked on various ways to mechanize mining. They have succeeded in many cases where the ore volume was sufficient to justify the high capital costs of equipment and the required infrastructures. Narrow-vein deposits, for their part, presented a greater challenge in terms of mechanization. Selective mining methods, such as shrinkage, were replaced by using a mechanized long-hole mining method. Despite all the efforts put into place, success stories remain rare. The difficulty in controlling wall stability following blast vibrations often resulted in high dilution, preventing narrow-veins extraction from being economically viable. Indeed, veins of small cross-section have in the past been uneconomical to mine since with the current mining methods a small vein necessitates the removal of a large quantity of waste rock on either sides of the vein. A large quantity of ore must then be processed to retrieve the small quantity of desired minerals.
Therefore, a great number of known narrow veins of mineralization are not presently mined since mining of such minerals is not economically viable due to the limitations of the present mining methods.
It is therefore an aim of the present invention to provide a new ore extracting process for allowing narrow veins of mineralization to be mined profitably.
It is a further aim of the present invention to provide a new and efficient mining approach for extracting ore from narrow-veins.
It is a still further aim of the present invention to optimize ore recuperation.
It is a further aim of the present invention to provide a new narrow-vein ore extraction process by which dilution from the walls of the vein is minimal.
Therefore, in accordance with the present invention, there is provided a method for extracting ore from an ore vein deposit, comprising the steps of a) establishing the location of the rock walls bordering the ore vein deposit, b) causing the ore comprised between the rock walls to spall into fragments, and c) retrieving the fragments.
In accordance with a further general aspect of the present invention there is provided a process for extracting ore from a vein having opposed sidewalls, comprising the steps of a) drilling pilot holes directly in the vein at specific intervals therealong, b) using thermal fragmentation, enlarging the pilot holes until the vein is fragmented, and c) recuperating the fragmented ore along the vein.
In accordance with a further general aspect of the present invention, there is provided a free-blast mining method for extracting ore from a vein having opposed sidewalls, comprising the steps of: locating the vein and determining the extent thereof, b) moving the burner at a controlled rate of travel between the sidewalls of the vein to cause the ore comprised in the vein to spall into fragments, and c) retrieving the fragments.
Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof, and in which:
It is a problem in the field of mining to economically extract high grade materials, such as gold, platinum, copper or other precious materials, from a narrow vein of mineralization. A narrow vein of mineralization is normally not commercially mined because the return in volume of useable mineral for the amount of ore removed and the amount of labor required to remove the ore render it uneconomical to retrieve the desired minerals in a narrow vein application. As will be seen hereinafter, the present invention provides a solution to that particular problem by significantly minimizing the dilution of the precious mineral into the surrounding waste rock during the extraction operation.
Unlike conventional mining methods which require that a great amount of commercially worthless rock (barren) be removed on either side of the vein due to the utilization of explosive charges, the present free-blast mining method provides for the removal of the true value only, i.e. the extraction of the mineral deposit from the surrounding environment. This may be readily appreciated from
In contrast, according to the present invention, pilot holes 18 (not blastholes) are defined directly in the vein 12 and subsequently enlarged or reamed by thermal fragmentation to the vein sidewalls 16, thereby avoiding dilution of the ore body contained in the vein in the commercially worthless matter located outwardly of the vein sidewalls 16. The trench can be kept as narrow as possible. This permits to extract 1 tonne of the desired mineral for 2 tonnes of gangue.
According to a preferred mode of extraction of the present invention, a first series 20 of three pilot holes 22, 24 and 26 are drilled directly into the vein 12 at predetermined longitudinal intervals, as shown in FIG. 2. The intervals are determined by the width of the vein 12. For a vein having a 12 inches (30 cm) width, the pilot holes are preferably of about 6 inches (15 cm) in diameter and spaced by a distance of about 21 inches (53 cm). Each pilot hole is between 40 feet (12 m) to 60 feet (18 m) deep and substantially center relative to a central axis of the vein 12. The broken material produced is recuperated and subsequently processed to separate the mineralized material from the barren.
The next step consists in the verification of the pilot holes 22, 24 and 26. In order to make sure that the pilot holes 22, 24 and 26 are in the vein 12, a conventional in-the-hole device (not shown) is used to locate the vein 12. Once the ore is located in the pilot holes 22, 24 and 26, thermal fragmentation is started to enlarge each pilot hole to the sidewalls 16 of the vein 12. In practice, it is understood that the pilot holes 22, 24 and 26 might in some instances be thermally reamed to a location which is located slightly outwardly of the sidewalls 16 of the vein 12, as shown in dotted lines in FIG. 2. Each pilot hole is enlarged by lowering a strong burner (not shown), powered by diesel fuel and air, into the hole and by igniting it. The burner could also be provided in the form of a plasma torch, especially in underground mining operations. The heat generated by the burner raises the temperature in the hole up to 1800° C. This creates thermal stresses that spall the rock. In simple terms, spalling is considered to be a form of decrepitation caused by an unequal expansion of rock crystals which overcomes molecule cohesion. The broken or fragmented material produced during this process ranges in size from fine grain to 4 cm (1.6 inch).
The first three pilot holes 22, 24 and 26 are preferably individually enlarged along all the length thereof from bottom to top in a predetermined sequence starting with the first hole 22, the third hole 26 and the second hole 24. The broken material produced during the thermal fragmentation operation of the first and third holes 22 and 26 is preferably left in the holes to act as a thermal barrier for preventing heat from escaping from the second hole 24 when the pillars of material separating the second hole 24 from the first hole 22 and the second hole 24 from the third hole 26 start to become fragmented, thereby allowing heat to pass from the second hole 24 to the first and the third holes 22 and 26. By leaving the fragmented material in the holes until the thermal fragmentation is fully completed in the adjacent hole, significant saving can be made in term of thermal energy consumption. As shown in dotted lines in
Thereafter, a second series 28 of pilot holes, comprising two longitudinally spaced-apart holes 30 and 32, are drilled directly in the vein 12 at the downstream end of the first series 20. The second pilot hole 32 of the second series 28 is first enlarged by thermal fragmentation followed by the first pilot hole 30. As for the first series 20, the fragmented material produced during the thermal fragmentation performed in each hole is preferably left in the hole and the first pilot 30 is enlarged to a greater extent than adjacent holes 26 and 32. As a general rule, the holes which are enlarged to a large size are always comprised between two pairs of pilot holes which have already been enlarged. As represented by reference numeral 34 further pairs of longitudinally spaced-apart pilot holes 36 and 38 are subsequently drilled and enlarged until the end of the vein 12 is reached.
Once the vein 12 has been fragmented on all the length thereof or along a sufficient portion thereof, the fragmented material is recuperated as by aspiration.
For deep veins extending more than 60 feet (18 m) deep into the surrounding strata, the waste rock surrounding the veins can be blasted after the ore contained in the first 60 feet (18 m) deep or so of the veins has been recovered as per the way described hereinbefore. In this way, the ore body of the vein can be fragmented and retrieved on another 60 feet (18 m) deep by repeating the above described steps from the new excavated bench level. It is understood that the 60 feet (18 m) deep is dictated by the limits of the drilling equipment and is only given for illustrative purposes.
As shown in
The second bench level 40 is formed by blasting the waste rock 42 surrounding the vein 12 after the ore body comprised in the first 60 feet (18 m) deep of the vein 12 has been retrieved from the first or surface level. After, the second bench level 40 has been excavated, the mining equipment, including the drill and the burner, is moved onto the platform of the second bench level 40 and pilot holes are drilled and enlarged by thermal fragmentation as per the way described hereinbefore. The fragmented material is retrieved as by aspiration and the site is further excavated to form a third bench level 44 to permit retrieval of the remaining deepest portion of the vein 12.
The above described thermal fragmentation mining method can be adapted to either surface or underground mining.
According to a further general aspect of the present invention, thermal fragmentation is used to carry out a channeling operation directly into the ore vein deposit to proceed with the extraction of the ore body from the surrounding waste rock without having to drill pilot holes into the vein.
As shown in
In summary, numerous advantages can be anticipated when looking at the present ore vein extracting process. In conventional selective mining, a portion of waste rock has to be included in the mineable reserves to allow sufficient space for equipment and workers. As illustrated in